According to the Associated Press, Zimmerman's wife called the police on her husband after she says he threatened her and her father. Just days ago, George Zimmerman's wife Shellie announced she was filing for divorce. The deputy police chief for Lake Mary told ABC News that "there was some kind of a domestic [incident]," adding, "we know that with his wife and father-in-law. Apparently there were some weapons involved and threats." Here's more from ABC, this time citing Shellie Zimmerman's version of the story, via her attorney Kelly Sims:

Zimmerman pulled a knife on [Shellie] today after she discovered a firearm in the house they shared. He then pulled a gun on his wife and her father after a verbal altercation.

Earlier, Police spokesperson Zach Hudson said that Zimmerman was in "investigative detention," meaning that he was detained on site while the officers complete their investigation of the incident — but he hasn't been arrested or charged with a crime. Hudson explained further:

"Anytime we have anybody suspected of doing anything, we place them in investigative detention until a complete investigation has been done."

Meanwhile, Zimmerman's brother Robert Zimmerman Jr. has already weighed in on the news:

We've learned from GZ case not to "jump to conclusions", to wait for facts, & to avoid speculation. "News" is a business - not your friend.